The invention relates to a process for the fluoriding of a catalyst.
For a number of catalytic processes, the suitability of the catalyst can be improved by incorporating fluorine therein. Incorporation of fluorine in catalysts can basically be effected in two manners. Fluorine can be incorporated in the catalysts during their preparation, for example by impregnation of the carrier with a suitable fluorine compound. It is also possible to incorporate fluorine in the finished catalyst prior to or during the initial phase of the process for which the catalyst is utilized, by addition of a suitable fluorine compound to a stream of gas and/or liquid which is passed over the catalyst. If desired, the latter fluoriding technique, which is generally referred to as in-situ fluoriding, may be combined with the impregnation technique mentioned before.
During in-situ fluoriding, fluorine produced by decomposition of the utilized fluorine compound under the prevailing reaction conditions is absorbed by the catalyst. In practice, the in-situ fluoriding process is continued until the catalyst has absorbed the calculated quantity of fluorine. In this case the conditions are so chosen that virtually all the fluorine supplied to the catalyst is in fact absorbed thereby.
During an investigation carried out by the applicant into the in-situ fluoriding of a fixed bed of catalyst particles, it has been established that the above-described technique as a rule leads to a non-uniform distribution of fluorine over the catalyst bed, with an excess of fluorine in the first part of the bed and a deficiency thereof in the final part of the bed. In processes where optimum catalyst performance is dependent on a given minimum quantity of fluorine on the catalyst, a non-uniform distribution of fluorine over the catalyst bed causes no harm, provided that the requisite minimum quantity of fluorine is present throughout the catalyst bed. In most cases, however, optimum catalyst performance is dependent on a given fixed fluorine content and the performance of the catalyst is worse if its fluorine content is above or below that fixed level.